This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | -2 |
| 3 | -6 |
| 4 | -10 |
| 5 | 20 |
| 6 | 352 |
| 7 | 2772 |
| 8 | 18132 |
| 9 | 104400 |
| 10 | 469608 |
| 11 | 238920 |
| 12 | -35811048 |
| 13 | -730972944 |
| 14 | -11436661728 |
| 15 | -164609993520 |
| 16 | -2294024595312 |
| 17 | -31488879303552 |
| 18 | -426338226719904 |
| 19 | -5626751283423072 |
| 20 | -70000948158061728 |
| 21 | -745703905072996800 |
| 22 | -4142683990211677440 |
| 23 | 110386551348875714880 |